A generator system for a gas turbine engine, such as that found in aircraft, ships, and some terrestrial and space vehicles, may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a generator control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter.
As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator, and this three-phase AC output can then be provided to a load such as, for example, an aircraft, ship, or vehicle electrical system.
Some of the mechanical components within the generator rotate and may thus be supplied with lubricant. In addition, some of the electrical components within the generator may generate heat due to electrical losses, and may thus be supplied with a cooling medium. The lubricating and cooling media may be supplied from different systems, or from a single system that supplies a fluid, such as oil, that acts as both a lubricating and a cooling medium. The lubricating and cooling medium supplied to the generator may flow into and through the shaft on which the main generator rotor is mounted, and be supplied to the various mechanical and electrical components via flow orifices formed in the shaft.
Among the electrical components that may generate significant amounts of heat during generator operation are the rotating rectifier circuits, which may be mounted within a hub that rotates inside the generator. In some generator configurations, the rotor shaft and hub may both include flow orifices, to allow the lubricating and cooling medium to be directly sprayed onto the rectifier circuits to provide sufficient cooling. In other generator configurations, sometimes referred to as “dry cavity” generators, the hub does not include such flow orifices. Thus, the rectifier circuits are not directly exposed to the lubricating and cooling medium. Instead, the rotating rectifier circuits are conduction cooled by the lubricating and cooling medium. More specifically, each rotating rectifier circuit may be mounted within the hub via a heat sink. The heat generated by each rectifier circuit is transferred to the lubricating and cooling medium flow in the shaft, via the heat sink, the hub, and the shaft, using conventional conduction cooling.
The exciter rotor mechanical design may be affected by several factors including, size envelope, peripheral speed, cooling efficiency, and rectifier diode rating. Thus, for a given cooling efficiency, if the rotating rectifier diode power density is increase, the size of the rectifier diodes may be increased, thereby increasing the size and weight of the exciter rotor and generator. Moreover, it has been found that the overall generator reliability has a direct correlation to the operating temperature of the rotating rectifier diodes.
Hence, there is a need for a generator that efficiently cools the rotating rectifier diodes, which allows the power density of the rectifier diodes to be increased without increasing the physical size of the rectifier diodes and/or without increasing the size and/or weight of the exciter rotor and/or without increasing the size and/or weight of the generator and/or without adversely affecting generator efficiency and/or reliability and/or hat allows a smaller diode package to be used for a given diode power density. The present invention addresses one or more of these needs.